Adsorbent Product for the Removal of Hydrocarbon Pollutants, and Method for Removing Hydrocarbon Pollution, In Particular at the Surface of the Water, Using Said Product

ABSTRACT

The adsorption properties of the adsorbent product, based on a porous mineral such as particularly pumice stone, result from the carbon formed on the walls of the pores of the mineral by cracking of an organic product, such as sugar or treatment plant sludges, previously impregnated in the pores of the mineral, the carbon thus formed making the product hydrophobic. After absorption of pollutant hydrocarbons by the product, the impregnated mineral is heated in a heat treatment unit, in the absence of oxygen, to bring it to a sufficient temperature to evaporate the hydrocarbons and/or decompose by cracking the organic product or hydrocarbon molecules and form or regenerate the carbon deposit. Application to the manufacture and to the recycling of an adsorbent product for the depollution particularly of bodies of waters or rivers polluted by hydrocarbons.

BACKGROUND

The present invention relates to a product intended to eliminatehydrocarbon pollutions which can particularly occur by the presence ofhydrocarbons in water, and to a process for using such a product. Theproduct of the invention is especially intended for the depollution ofseas, rivers or lakes polluted by hydrocarbons but can also be used intreatment plants, car parks, garages and all places where hydrocarbonpollution occurs.

Depollution by adsorption methods are already well known. Generally,adsorption is a physical phenomenon which fixes molecules on the surfaceof a solid called adsorbent. This phenomenon is used to recoverundesirable fluid, liquid or gaseous molecules dispersed in anotherfluid or solvent such as water or air.

The adsorbent which is principally used in practice is active carbon.Adsorption on active carbon is intended to treat organic matters notfound in high quantities in the solvent. The active carbon is commonlyused therefore for many filtering applications in which the fluid, wateror air, passes through a filter charged with active carbon as describedin FR 2107069.

Other absorbent products are known, for example by GB 1204353 or FR2137531 which describes a porous alumina including carbon formed on thewalls of the pores. However, this product, by its particle size and itsdensity does not allow a hydrophoby and a sufficient buoyancy to beensured for the targeted application.

Other absorbent products are also known, more suitable to a fluidabsorption use, especially hydrocarbons, by spreading them over thesurfaces covered by the said hydrocarbons. These products can besynthetic, based on materials of mineral origin, vegetal origin andpolymers. However, most of these products rapidly release the absorbedhydrocarbons which makes them not very efficient and complicates theiruse. Moreover, almost all of these absorbent products can be used onlyonce. After use, they are often burnt or dumped in technical burialcentres which creates other forms of pollution. Lastly, some of theseproducts do not float and among those which do, the buoyancy is verylimited over time.

Document DE 3142275 describes a pollutant hydrocarbon recovery processby use of pumice stone as absorbent and treatment of this stone when itis impregnated with hydrocarbons by centrifugation and distillation heattreatment. However, the product used is not hydrophobic and its buoyancyis insufficient. Although it allows hydrocarbons to be recovered byadsorption, the treatment of the charged product at best allows aregeneration to original condition to be ensured and therefore with thedisadvantage of an insufficient hydrophoby and buoyancy implyingdifficulties in recovering the product charged with hydrocarbons and arelatively low adsorption rate efficiency.

For applications of the type mentioned above, the absorbent and/oradsorbent product must combine the following various properties:

-   -   on the one hand, a sufficient hydrocarbon adsorption capacity        and, on the other hand, minimum water absorption so that the        adsorbent product charged with the maximum possible amount of        hydrocarbons can be recovered,    -   maximum buoyancy to allow the product to remain in contact with        the pollutants as long as possible, avoiding that the product        falls to the bottom of the water, even when charged with        pollutants, to facilitate its recovery,    -   possibility of treatment and recycling after adsorption        especially including: the recovery of the product containing the        adsorbed hydrocarbons, its treatment to prevent secondary        pollution by the recovered hydrocarbons and, preferentially, the        recycling of the adsorbent product and, possibly, of the        absorbed pollutants.

One of the important features is therefore that the product be ashydrophobic as possible. However, the products or techniques used tomake the basic product hydrophobic are often very expensive.

Certain known products are hydrophobic and have hydrocarbon adsorptioncapacities which are considered very high. They also have a fairly lowdensity allowing them to float on the water and thus facilitate theirrecovery. Products of this type are particularly described inFR-A-2105752, FR-A-2065206, JP-A-56078628, JP-A-11076811.

Moreover, a pumice stone which has a carbon content greater than 5% andspecific hydrocarbon adsorption properties whilst being hydrophobic isalso known. The time this pumice stone stays on the surface of the bodyof water to be depolluted is between two minutes and eight hours,especially between three minutes and two hours. These relatively shorttimes may be insufficient to adsorb a maximum of hydrocarbons. Also,this creates a constraint concerning the recovery of the pumice stonewhich must be done therefore relatively quickly after it has been spreadand in a time also fairly short. Failing this, the insufficient buoyancyof such products means that a substantial part of the adsorbent productmay be immersed before it can be recovered. What is more, these productsare manufactured by the absorption of hydrocarbons then calcination togenerate the carbon deposit required on the walls of pores of the pumicestone to make it adsorbent and hydrophobic. The manufacture of theproduct itself is therefore a source of pollution.

The recycling of the pumice stone after adsorption of the hydrocarbonsand recovery on the surface of the water is done by calcination toevacuate the adsorbed hydrocarbons. This has the advantage of being ableto possibly reform the carbon layer on the walls of the pumice stone andtherefore to make it again directly usable. But this also poses theproblem of correct control of the combustion as this is done at hightemperature, and of the control of the atmosphere in the calcinationoven to obtain a homogeneous product, and of the treatment of the fumes.

SUMMARY OF THE INVENTION

The aim of the present invention is to solve the problems mentionedabove and especially to allow the manufacture of an adsorbent productespecially adapted for the depollution of bodies of water or similar byadsorption of the surface hydrocarbons. Its aim is to facilitate themanufacture of such a product by the use of a process less pollutingthan those used previously. Its aim is also to improve the efficiencyand the yield of the product and its recycling.

With these targets in mind, the subject of the invention is an adsorbentproduct for the elimination of hydrocarbon pollutions especially presenton the surface of water, this product being based on a porous mineralthe adsorption properties of which result from the carbon formed on thewalls of the pores of the said mineral. According to the invention, theproduct is characterised in that the porous mineral is pumice stone orperlite and the carbon formed on the walls of the pores is obtained bycracking of an organic product previously impregnated in the pores ofthe said mineral, the resulting product being hydrophobic.

The organic product preferentially mainly consists of sugar or treatmentplant sludges. By sugar, we in particular mean common sugar orsaccharose but also the various similar organic compounds includingsaccharose and other mono, bi or polysaccharides.

The porous mineral is particularly pumice stone or perlite or zeolite.

The aim of the invention is also a process for eliminating hydrocarbonpollutions, especially present on the surface of water, characterised bythe use of an adsorbent product such as defined above and in that, afterthe adsorbent product has been spread on the pollutant hydrocarbons andhas adsorbed the said hydrocarbons, the product impregnated withhydrocarbons is placed in a heat treatment unit brought, in the absenceof oxygen, to a predetermined temperature such that the hydrocarbons areevaporated and the product is thus returned to its initial and reusablestate which enables it to be recycled.

Preferentially, the treatment temperature is from 200 to 450° C.

The specific heat treatment according to the process of the inventionconsists in fact in ensuring the elimination by evaporation of thegreater part of the hydrocarbons absorbed in the product and also inregenerating, as required, the carbon deposit on the surface of thewalls of the pores of the porous mineral used.

Another specific feature of the process lies in the process forobtaining the product defined above according to which the carbon formedon the walls of the pores of the said porous mineral is formed bycracking of molecules of an organic product previously impregnated inthe pores of the said mineral, this organic product being preferentiallysugar or treatment plant sludges.

The porous mineral chosen is preferentially pumice stone of a calibrebetween 60 microns and 16 mm and a grain density lower than 700 kg/m3and an unpacked dry density lower than 350 kg/m3. After selection of thestones with required characteristics, the foreign stones and the dustare separated from the pumice stone, by techniques of known types, suchas washing and flotation for example, then the pumice stone is dried sothat its humidity ratio will be lower than 40%.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

According to a specific embodiment, the porous mineral thus prepared isimmersed in a liquid mix including water and sugar to impregnate thesaid mineral with the said mix then the impregnated mineral is heated ina heat treatment unit, in the absence of oxygen, to bring it to asufficient temperature to decompose by cracking the sugar molecules andtherefore form a carbon deposit on the walls of the pores of the porousmineral.

Preferentially,

-   -   the liquid mix includes 10 to 20% of sugar in weight,        preferentially 15 to 20%,    -   the liquid mix also includes lemon juice, in a proportion of        around 1% in weight, which allows the sugar to be diluted        uniformly in the water,    -   the liquid mix can also include a low proportion of gas-oil of        around 0.5 to 1%,    -   the impregnation time is typically around several minutes,        between 3 and 10 minutes, for example around 5 minutes,    -   the heating temperature is typically between 500 and 600° C.,        sufficient to ensure the evaporation of the other components of        the mix and the cracking of the carbonated molecules,    -   a nitrogen atmosphere is maintained in the oven replacing the        oxygen.

The adsorbent product obtained typically has a carbon ratio of 2 to 4%in weight. The product thus ready for use allows, according to theviscosity of the hydrocarbons, and according to the time the productremains in contact with the polluted water, the adsorption ofhydrocarbons at a ratio typically higher than 15% of its volume, and canreach 25% or even more.

Preferentially, as stated above, a liquid mix will be used especiallyincluding sugar. However, treatment plant sludges can also be used.Indeed, the use of treatment plant sludges has the advantage that theyinclude organic matters in the molecules in which the number of carbonatoms is high thus forming long molecular chains which enable, duringcracking, a lower loss of carbon. Comparatively, organic matters inwhich the number of carbon atoms is relatively low, such as C8H18 forexample, immediately vaporise during cracking. When the number of carbonatoms increases, for example C11-H22-O11, the evaporation is lower andtherefore the quantity of carbon which can remain on the walls of thepores of the porous material increases. Thus, the carbon ratio remainingin the pumice stone after cracking done on the pumice stone impregnatedwith petrol is only 2%. With a sugar solution, according to theinvention, this ratio increases to around 25%. By using treatment plantsludges, general formula of C20-H40-O_(x)N_(y)P_(z) type, this ratio canreach around 80%. This high ratio would be especially advantageous.However, these sludges can fairly often contain products such as heavymetals which are dangerous for human health and the environment.Consequently, during the cracking, the gases given off must then becaptured and treated which reduces the economic interest of the process.Also, certain sludge components, such as these heavy metals, couldresist the heat treatment and thus remain in the pumice stone. Thus, inspite of the interest of these sludges, sugar will generally bepreferred as organic product used according to the invention.

In the global process according to the invention, apart from theinterest of the process to obtain the original product, anotherespecially advantageous aspect concerns the recycling of the productafter the said product has absorbed the pollutant hydrocarbons. Duringthe heat treatment operation, similar to the cracking of sugar done forthe preparation of the new product, the hydrocarbons absorbed in theproduct evaporate and regenerate, if required, by cracking of the saidhydrocarbons, the carbon deposited on the walls of the pores. Thepollution products stored in the adsorbent product are thus eliminatedfrom it and it is returned more or less to its initial condition againready for a new use. Moreover, the evaporated hydrocarbons can becaptured and treated by a condensation system and recovered for apossible use.

Other features and advantages of the invention will become apparent onreading the following description of a typical example of all themanufacturing, use and recycling operations for the product according tothe invention.

First of all, 1 m³ of pumice stones was taken with a calibre greaterthan 2 mm and an unpacked dry density lower than 300 kg/m³. Among thesepumice stones, those which had grain densities lower than 600 kg/m³ werechosen.

The pumice stones were then cleaned by washing and flotation, then thepumice stones were dried so that their humidity was around 20%.

To prepare the effective liquid mix for around 1 m³ of pumice stones, aconcentrate was first prepared by mixing 47.5 kg of water, 50 kg ofsugar in powder form and 2.5 kg of lemon juice. This mix was mixed for15 to 30 minutes until the sugar was uniformly dissolved.

The effective liquid mix was obtained at time of use by adding 150 kg ofwater to the concentrate in a container of suitable capacity.

The pumice stones were placed in a perforated receptacle which wasplunged into the container containing the liquid mix for 5 minutesduring which the pumice stones were impregnated with the said mix.

The perforated receptacle was removed from the liquid mix and the pumicestones left to drip to lose the excess liquid mix.

The pumice stones were then placed for 15 minutes in an oven from whichall the oxygen had been driven out and replaced by nitrogen. Thetemperature of the oven was maintained to 550° C. After these 15 minutesat 550° C., the pumice stones were removed from the oven and left tocool.

The carbon content measured was then 3%.

To measure the degree of hydrophoby of the pumice stone obtained, asample was placed in water for 3 minutes. After this time, the stoneshad absorbed less than 4% of water. The tests were extended up to 7 daysof immersion in water. The pumice stones still had not absorbed morethan 4% of water and less than 2% in weight had sunk.

Then, diesel fuel was made absorbed by these pumice stones. It wasobserved that after 4 minutes they had absorbed around 20% of theirvolume.

This batch of pumice stones impregnated with diesel fuel was then placedin the same oven as mentioned above, with the oxygen replaced bynitrogen, and the temperature was increased to 450° C. and the pumicestones left at this temperature for 20 minutes. It was then observedthat the hydrocarbons contained in the pumice stones had evaporated.There is no calcination of the product but only heating of the product.

The pumice stones which had been subjected to this heat treatment wereagain used for another diesel fuel depollution operation and the sameadsorption characteristics were observed, renewed after having repeatedthis test around ten times.

It was thus demonstrated that the process according to the inventionallows porous minerals, and especially pumice stones, to be renderedhydrophobic by a technique which creates no environmental problems.Also, the buoyancy of pumice stones even charged with hydrocarbons wassubstantially greater than that of earlier products thus enabling a fastresponse on a body of water to be treated by depositing pumice stoneaggregates and recovering them several days later. Also, the productaccording to the invention is almost indefinitely recyclable by thehydrocarbon desorption process without combustion which also allowssecondary pollution problems to be avoided. Moreover, it can allow arecovery at least partial of the hydrocarbons by condensation of thegases given off by the heating of the pumice stones impregnated withhydrocarbons in an oxygen-free atmosphere.

Other tests have been done using treatment plant sludges as organicmaterial for the preparation of the adsorbent product. The sludges usedcontained 20% of solid matter and 12% of organic matter. 200 litres ofthese sludges were mixed with 280 litres of water for 3 to 6 minutes.When this mix was homogeneous, the pumice stones were impregnated in itas described in the first example and the process was continued in thesame manner.

In dried sludges, the organic matters contain 20 to 35% of elementarycarbon. In sugar, this ratio is around 40%. But, as stated previously,the length of carbonated chains is higher in sludges which enables alower loss of carbon during cracking. Thus, it was observed that thecarbon loss during the cracking in this second example, with the use ofsludges from biological treatment, is of 15 to 33%, whereas it is around50 to 75% with the sugar-based mix of the previous example. In spite ofthis relative advantage, the use of sugar is still preferred for thereasons given above.

The invention is especially intended for the depollution of bodies ofwater, seas, rivers, etc., polluted by hydrocarbons but it can also beused, for example, in refineries to separate water from petrol or toabsorb other chemical products. The product obtained according to theinvention can also be used generally in the filtration domain. Accordingto various applications, certain features of the product could beadapted, such as its particle size for example, or its carbon content.Lastly, the pumice stone can also be replaced by other minerals such asespecially porous volcanic rocks such as perlite or zeolite.

1-13. (canceled)
 14. An adsorbent product for the elimination ofhydrocarbon pollutions present on the surface of water, said productbeing based on a porous mineral having adsorption properties whichresult from carbon formed on walls of pores of the porus mineral, theporous mineral being one pumice stone and perlite, the carbon formed onthe walls of the pores being obtained by cracking an organic productpreviously impregnated into the pores of said mineral, and the productbeing hydrophobic.
 15. The product according to claim 14, wherein theproduct is an organic product consisting mainly of one of sugar andtreatment plant sludges.
 16. A process for eliminating hydrocarbonpollutions present on the surface of water, comprising using theadsorbent product according to claim 14, spreading the adsorbent producton pollutant hydrocarbons, adsorbing the hydrocarbons, using saidadsorbent product, placing the product impregnated with saidhydrocarbons in a heat treatment unit brought, in the absence of oxygen,to a temperature of 200 to 450° C., and evaporating the hydrocarbons sothat the product is thus returned to an initial condition and reusable.17. The process according to claim 16, further comprising treating theevaporated hydrocarbons with a condensation system and recovering theevaporated hydrocarbons.
 18. The process according to claim 16, furthercomprising obtaining the adsorbent product, by forming carbon on thewalls of the pores of the porous mineral by cracking molecules of anorganic product previously impregnated in the pores of the mineral. 19.The process for obtaining an adsorbent product according to claim 14,comprising forming carbon on the walls of the pores of the porousmineral by cracking molecules of an organic product previouslyimpregnated in the pores of the mineral.
 20. The process according toclaim 18, wherein the organic product consists mainly of one of sugarand treatment plant sludges.
 21. The process according to claim 20,further comprising, during the preparation of the product, immersing theporous mineral in a liquid mix including water and the organic productto impregnate the mineral with the mix and heating the impregnatedmineral in a heat treatment unit, in the absence of oxygen, to bring theimpregnated material to a sufficient temperature to decompose bycracking the molecules of the organic product and form a carbon depositon the walls of the pores of the porous mineral.
 22. The processaccording to claim 21, further comprising using a liquid mix including10 to 20% of sugar in weight.
 23. The process according to claim 21,further comprising using a liquid mix including lemon juice.
 24. Theprocess according to claim 21, comprising using an impregnation timebetween 3 and 10 minutes.
 25. The process according to claim 21,comprising using a heating temperature between 500 and 600° C.
 26. Theprocess according to claim 21, further comprising maintaining a nitrogenatmosphere in the heat treatment unit.